JPS589633B2 - Multi-burst Shingouno Shinpukuhourakusenkenshiyutsusouch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting the amplitude envelope of a multi-burst signal included in a television video signal.

In order to measure frequency amplitude distortion characteristics in a high image frequency band in a television signal transmission system, there is a method of using a multi-burst signal used as a vertical blanking interval insertion test signal (so-called VITS).

As shown in FIG. 1, this signal is, for example, 0. 5MHz,
1.0 MHz, 2.0'MHz13. 5 8
Multi-frequency equal-amplitude sine wave bursts of MHz and 4.2 MHz are arranged in order within a horizontal scanning period, and frequency-amplitude distortion characteristics can be measured from the amplitude changes of each.

Traditionally, it has been common practice to use a broadband oscilloscope to visually read the envelope for this measurement.
DC level fluctuations caused by changes in the average brightness of the video signal, and because this multi-burst signal is inserted into a small portion of the vertical blanking period, the time axis of the oscilloscope is expanded, causing the normal brightness to change. Due to the fact that it becomes darker, it is difficult to measure and the measured values tend to contain errors.

Therefore, in order to make this measurement easy and accurate, there is a method in which the multiburst signal is directly converted into digital data using an analog-to-digital converter with high-speed processing capabilities, and then processed using a computer to calculate the frequency characteristics. is also being implemented.

However, since the frequency range of the multiburst signal is from several hundred KHz to 4-5 MHz, this method requires an analog-to-digital converter with ultra-high-speed processing capability, making it extremely expensive. was there.

In order to eliminate this drawback, the purpose of the present invention is to convert a multiburst signal into an amplitude envelope signal as shown in FIG.
An object of the present invention is to provide a detection device to which a digital converter can be applied.

The gist of the present invention to achieve this object is to detect the position of the positive peak point of the multi-burst signal before phase shifting from the waveform obtained by shifting the phase of the multi-burst signal consisting of a sine wave, and to generate a sampling pulse. A sample in which the multi-burst signal and the sampling pulse are input to the source and gate of a field-effect transistor, respectively, and a capacitor is connected to the drain, and the output terminal is taken out between the capacitor and the drain. The present invention provides an amplitude envelope detection device for a multi-burst signal, which includes a hold circuit, sequentially samples and holds positive peak values of the multi-burst signal, and outputs the sampled and held signals as an envelope voltage.

To obtain the envelope signal, connect diode 1 as shown in Figure 3.
, a peak value holding circuit consisting of a capacitor 2 is normally used.

For example, when the step input voltage shown in FIG. As shown in the output waveform, the voltage at the output terminal 0 increases, and if the diode 1 has no forward voltage drop, this voltage approaches the input voltage value as much as possible.

Thereafter, even if the input voltage is lowered, the voltage applied to the diode 1 will be in the opposite direction, so if the reverse resistance RB of the diode 1 is assumed to be infinite, the voltage before the input voltage was lowered will be maintained.

However, in reality, RB has a finite value, and the voltage at the output terminal O gradually decreases with time.

Furthermore, the internal resistance RD of diode 1 changes depending on the voltage across diode 1, and increases as the voltage difference becomes smaller. Therefore, as the output voltage in Figure 4 approaches the input voltage value, the charging time constant becomes longer and the charging time constant increases gradually. rise to

In order to apply the circuit shown in Fig. 3 to the detection circuit, a transistor 3 is connected between the diode 1 and the capacitor 2 as shown in Fig. 5, and a positive pulse of a specific time width is applied to the input terminal 2. Then, the transistor 3 becomes conductive, and due to its low internal resistance, the voltage held in the capacitor 2 is rapidly discharged, and the voltage at the output terminal O becomes Ov.

Next, when the voltage at the input terminal I2 becomes OV, the transistor 3 is cut off, and the voltage at the output terminal O rises in accordance with the voltage applied to the input terminal 1.

Therefore, let's consider detecting the envelope of a multiburst signal using this circuit.

The multi-burst signal waveform shown in FIG. 6a is applied to the input terminal (1) in FIG. 5, and a positive pulse is applied to the input terminal (2) at the division of each frequency range as shown in FIG. 6 (b).

The voltage waveform at the output terminal O varies depending on the charging time constant. For example, if the charging time constant is longer than the 1/2 cycle time of a 0.5 MHz burst sine wave, the voltage waveform at the output terminal O is approximately equal to the 1/2 cycle time as shown in Figure 6C. In this case, there is a discharge because the reverse resistance RB of the diode 1 has a finite value, as shown in FIG. 6d.

The charging time constant is determined by selecting the capacitance C of capacitor 2 appropriately because the forward resistance RD of diode 1 is a value unique to the diode, but as long as diode 1 is used, it is shown in Figure 6a. It is impossible to maintain the peak value of a multi-burst signal containing a sine wave, which exists for only a few cycles within such a limited time, for a sufficient period of time.

Since it is inappropriate to simply use the conventionally known peak value holding circuit, the present invention provides a multi-burst signal generated by a sampling pulse generation circuit, as shown in the block diagram of FIG. Add the sampling pulse located at the positive peak point of the signal to the sample hold circuit,
A sample-and-hold circuit mainly composed of field-effect transistors with constant internal resistance and small size holds the positive peak value of the multiburst signal according to the sampling pulse, and is configured so that its output becomes an envelope. It is.

The configuration of the sampling pulse generation circuit is, for example, as shown in Fig. 8, in which a multiburst signal is input to a 90 degree phase shift circuit, its output is connected to an amplitude limiting circuit, and the output is added to a Schmitt trigger circuit. Divide the output into two branches, input one to the delay circuit, and connect the other to the inversion circuit.
These outputs are input to an AND circuit and the output is used as a sampling pulse.

To explain the operation with reference to the waveform in FIG. 9, the multi-burst signal shown in FIG. 9a is converted to the 90-degree advanced waveform shown in FIG. 9b by a 90-degree phase shifter using a differentiating circuit. be done.

However, since each amplitude of the converted differential waveform increases in proportion to the frequency, if the upper and lower limits are cut by an amplitude limiting circuit, a waveform of uniform amplitude as shown in FIG. 9C is obtained.

When a Schmitt trigger circuit detects a point passing through zero potential in this waveform, its output becomes the waveform shown in FIG. 9d.

On the one hand, this waveform is added to a delay circuit that slightly delays it to form the waveform shown in Figure 9e, and on the other hand it is input to an inversion circuit to form the waveform shown in Figure 9f, and when these waveforms are added to an AND circuit, the waveform shown in Figure 9 is obtained. A sampling pulse corresponding to the positive peak point of the multiburst signal before phase shifting and a sampling pulse corresponding to the frequency switching point of the multiburst signal as shown in g are obtained.

However, the latter sampling pulse at the time of frequency switching is not necessarily necessary, and even if this pulse is omitted, the low-level division between each frequency will simply disappear in the amplitude envelope shown in FIG. 2.

Next, the sample and hold circuit connects the multi-burst signal input terminal i1 to the source S of the field effect transistor 4, as shown in FIG. 10, and inputs the sampling pulse generated by the sampling pulse generation circuit to the gate G. The capacitor 2' is connected to the drain D, the other end is grounded, and the envelope voltage output terminal O is taken out from between the drain D and the capacitor 2'.

In a field effect transistor, when the drain-source voltage is approximately 1V or less, the drain voltage VD and drain current D are proportional as shown in Figure 11, and therefore the internal resistance is influenced by the drain-source voltage. The internal resistance value is also much smaller than the forward resistance value RD of a diode, which is several Q.

Therefore, even if the difference between the input and output voltages becomes small, the charging time constant does not change and can be made small.

Taking advantage of this feature, connect the input terminal 1 as shown in Figure 10.
If the multi-burst signal shown in FIG. 12a is added to 1, and the sampling pulse shown in FIG. An amplitude envelope signal that maintains the positive peak voltage of the multiburst signal shown in FIG. 1 is obtained, and the multiburst signal shown in FIG. 1 is converted as shown in FIG. 2.

Actually, the delay circuit in the sampling pulse generation circuit,
Since the timing of sampling pulse generation is slightly delayed from the peak point due to response time, etc., it is necessary to delay the multi-burst signal to the sample and hold circuit by that amount.
Alternatively, it becomes necessary to adjust the phase shift angle within the sampling pulse generation circuit.

FIG. 13 is a circuit diagram specifically showing an example of the detection device of the present invention.

As described above, by using the detection device according to the present invention, the peak value can be maintained during the limited sine wave burst period, and the frequency amplitude distortion characteristics can be digitally converted using a relatively slow analog-to-digital converter. can be processed.

Specifically, when comparing the required processing speeds of analog-to-digital converters, if performance in a frequency range twice the processing frequency is required for sampling, the conventional direct conversion method can process multiburst signals at To process a 5 MHz sine wave burst, an 8-10 MHz band converter would be required.

However, if the device according to the present invention converts into an envelope, the retention time of each burst is about 7 μs, so a converter of about several hundred KHz is sufficient, and it is clear that there will be a considerable difference in price. be.

In addition, the output of this detection device does not necessarily need to be digitally processed, but it is also possible to differentially compare the white signal and analog amount for each burst, which is an envelope signal, by using two timing pulse circuits and two timing pulse circuits. Measurement is possible by adding a hold circuit, a comparison circuit, and an output display circuit.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram of the multi-burst signal, Fig. 2 is a waveform diagram of the envelope obtained by the detection device according to the present invention, Fig. 3 is a configuration diagram of the peak value holding circuit, and Fig. 4 is an explanation of its operation. figure,
FIG. 5 is a block diagram of the peak value holding circuit, FIG. 6 is an explanatory diagram of its operation, FIG. 7 is a block diagram of the detection device according to the present invention, and FIG. 8 is a block diagram of the sampling pulse generation circuit. Fig. 9 is an explanatory diagram of its operation, Fig. 10 is a configuration diagram of the sample and hold circuit, Fig. 11 is a characteristic diagram of a field effect transistor, Fig. 12 is an explanatory diagram of the operation of the sample and hold circuit, and Fig. 13 is a diagram of the operation of the sample and hold circuit. It is a block diagram of the circuit of such a detection device, and FIGS. 8 to 10, FIG. 12, and FIG. 13 are drawings showing examples. 2 is a capacitor, 4 is a field effect transistor, and D, S, and G are the drain, source, and gate of the field effect transistor, respectively.

Claims (1)

[Claims] 1. A sampling pulse generation circuit that generates a sampling pulse by detecting the position of the positive peak point of the multiburst signal before phase shifting from the waveform obtained by shifting the phase of the multiburst signal consisting of a sine wave, and a field effect type The multi-burst signal and the sampling pulse are input to the source and gate of the transistor, respectively, and a capacitor is connected to the drain, and a sample-hold circuit is provided in which the output terminal is taken out from between the capacitor and the drain. An amplitude envelope detection device for a multi-burst signal that sequentially samples and holds the peak value of and outputs it as an envelope voltage.